1. Field of the Invention
This invention relates to a suspension system for a vehicle having a suspension arm member whose inner end is supported, at two points spaced apart in a longitudinal direction of the vehicle body, by a vehicle body member and an assist link, particularly to a measure by which setting for riding comfort and driving stability can be changed as desired.
2. Description of the Prior Art
The Japanese Utility Model Registration Application Laying Open Gazette No. 64-49404, for example, discloses a suspension arm member whose inner end is supported swingably, at two points spaced apart in a longitudinal direction of the vehicle body, to a vehicle body member through the medium of bushes (each having an axial center extending in horizontal direction) and whose outer end is supported swingably to a wheel support member and an assist link fixed swingably to an intermediate part of the suspension arm member and to the vehicle body member, in which a support center of the assist link on the vehicle body side is positioned on the axial center of the bush of the suspension arm member.
In the above case, provision of the assist link heightens effectively the lateral rigidity of the suspension arm member which resists external force from the vehicle width direction at turning of the vehicle body, for example, and thus driving stability at turning is improved. Provision of the assist link also makes it possible to utilize a softer bush near the assist link, whereby input from a longitudinal direction of the vehicle body which acts when a vehicle runs over roughness of the road, for example, is let escape by moving the wheel positively in front and rear direction and as a result, compliance in front and rear direction is ensured and riding comfort is improved.
Recently, it has been demanded to toe-control the wheel positively in response to its bumping at turning or at running over roughness of the road and to camber-control positively the camber angle (an inclining angle of the wheel in relation to a vertical line of the wheel support member). More particularly, it has been demanded to change properly and freely the toe-control and the camber-control of the wheel which bumps at turning, at running over roughness of the road, etc., according to characteristics of each kind of vehicle by directing the bumping wheel to an oversteering tendency (turning ability at turning is heightened) by making it toe-in, by directing it to an understeering tendency (driving stability at turning is heightened) by making it toe-out, by heightening the straight driving stability by making the camber angle of the wheel larger, by heightening comfortableness to ride in and lightening steering wheel holding power at turning by making the camber angle of the wheel smaller, etc.
In the above-mentioned conventional suspension system, however, since the support center on the vehicle body side of the assist link is positioned on the axial center of the bush, the swinging locus in vertical direction of the suspension arm member and that of the assist link coincide with each other and therefore, the wheel which bumps at turning, at running over roughness of the road, etc., only swings in vertical direction with the support parts (on the vehicle body side) of the suspension arm member and the assist link as fulcrums. Thus, it is impossible to effect the positive change of toe-control and camber-control at bumping of the wheel.
In the above-mentioned suspension system, since the support part (on the vehicle body side) of the suspension arm member is supported by the vehicle body member through the medium of a bush or the like, even if a bush close to the assist link (out of the bushes of two support parts on the vehicle body side) is made soft, quantity of moving the bumping wheel rearwardly against input from the front of the vehicle body when a vehicle runs over roughness of the road, for example, becomes very small. Therefore, there is a limit in ensuring the compliance, when input from the front of the vehicle body acts, by softness of a bush close to the assist link. Thus, it is impossible to ensure full riding comfort when the vehicle runs over roughness of the road, for example.